Quantum cascade lasers (QCL) have long been considered as a natural concept of terahertz devices. Like many lasers widely used in visible to infrared wavelengths, quantum cascade lasers are based on semiconductor materials. But quantum cascade lasers work entirely differently than the typical semiconductor lasers used in barcode readers or laser Pointers. In short, quantum cascade lasers are built from a precisely designed stack of repeated semiconductor structures (see figure c), designed to achieve appropriate electron transitions
The concept of a quantum cascade laser was proposed in 1971, but it wasn’t first demonstrated by Faist and his colleagues until 1994, and then by bell LABS in the United States. This method provides value for many basic experiments and application experiments, especially the infrared band. Since 2001, quantum cascade lasaerpointers for terahertz emission have also made substantial progress. But the need for cryogenic coolants, usually liquid helium, has greatly increased the complexity and cost of the devices and made them larger and less mobile, preventing their widespread use. Seven years ago, the operating temperature reached about 200K (-73 ° c), and the pursuit of running terahertz quantum cascade lasers at higher temperatures stalled there.
Break down the barriers that depend on cryogenic technology
Reaching 200K is an impressive feat. This is just below the threshold where thermoelectric refrigeration can replace cryogenic technology. Since 2012, the temperature record has not changed, which means that some kind of “psychological barrier” has been set up, and many scenarios begin to accept that terahertz quantum cascade lasers must work with cryocoolers.
Now the ETH team has cracked that barrier. In the journal Applied Physics Letters, they propose a thermally cooled terahertz quantum cascade laser that works at 210 kelvin. In addition, the laser is strong enough to be measured with a room-temperature detector. This means that the whole device can work without cold cooling, further enhancing the potential of this method in practical applications.